1. Field of the Invention
This invention relates to multipurpose oil-soluble additives for lubricating oils which have utility to impart to an oil when incorporated therein an improved viscosity index and/or sludge dispersancy and/or pour point depressancy and/or oxidation stability and to the preparation of such additives. Broadly, the novel additives are polymers prepared by hydrolysis of an anionic-graft polymer obtained from polymerization of nitrile monomers containing at least one vinylidene group onto an anion of an oxidized copolymer of ethylene and propylene. The present invention teaches the additional use of these hydrolyzed anionic graft polymers as precursors for post polymerization functionalization.
2. Description of the Prior Art
The literature abounds with discussions of multifunctional viscosity index (V.I.) improvers usually containing nitrogen to enhance their dispersant activity including polymeric nitrile-containing substances as lubricanting oil additives with detergent-dispersant and other properties.
The preparation of such multifunctional V.I. improving polymeric substances according to the prior art included: copolymerization of one or more olefins with a nitrile-containing monomer (U.S. Pat. No. 3,445,387); free radical-grafting of a hydroperoxidized ethylene copolymer with a polar vinylidene monomer, such as acrylonitrile (see U.S. Pat. No. 3,404,091); reacting a nitrile-containing compound with a reactive copolymer such as is obtained from free radical-grafting of maleic anhydride to polyisobutylene (see U.S. Pat. No. 3,488,049); reacting an alkenyl cyanide with an alkenyl amine and a hydrocarbon-substituted succinic acid-producing compound (see U.S. Pat. No. 3,278,550); free radical-grafting an ester of an amino alcohol onto an oxidized interpolymer of ethylene and propylene (see U.S. Pat. No. 3,687,849); thermally reacting amines with an oxidized ethylene-propylene copolymer (see U.S. Pat. No. 3,864,268); and, by hydrolysis of the free radical graft of acrylonitrile onto ethylenepropylene copolymer (see U.S. Pat. No. 3,326,804).
These processes which utilize free radicals have certain disadvantages including irreversible crosslinking of the copolymer and homopolymerization of monomeric components. The crosslinking disadvantage is shown in U.S. Pat. No. 3,236,917 wherein initiation of the desired addition reaction by generation of free radicals also provokes grafting of a single molecule of maleic anhydride into two copolymer chains thereby irreversibly crosslinking the copolymer and markedly decreasing its solubility in oil. One approach to overcoming this disadvantage is shown in U.S. Pat. No. 3,378,492 which teaches grafting an unsaturated hydrocarbon polymeric compound, e.g. polybutadiene, directly with an unsaturated, polar, nitrogen-containing organic compound, e.g. acrylonitrile.
Another approach to preparing an oil-soluble nitrogeneous ashless dispersant involves reacting an alkali metal salt of a long-chain ketone with acrylonitrile (see U.S. Pat. Nos. 3,565,803 and 3,723,501). Unfortunately, formation of the dialkyl ketone precursor is by ozonization which is an expensive and hazardous process involving dimethyl sulfide, an environmentally toxic agent. Also taught as a multifunctional additive for lubricating oils is the anionic-graft polymer of a lithiated ethylene-propylene-hexadiene terpolymer with an amino methacrylate monomer (see U.S. Pat. No. 3,879,304).
It is well known and widely practiced in commerce to provide lubricants with improved dispersancy by the addition of metal free dispersants of the acylated amine types as described in U.S. Pat. No. 3,272,746 wherein such dispersants are stated to be characterized by the structural presence of a substantially saturated hydrocarbon polar group of the class of acyl, acylimidoyl and acyloxy radicals having a nitrogen atom attached directly to said group.